Heads Up Display Pilots - Question
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Heads Up Display Pilots - Question
1. What is the definition of the angle made between the Flight Path Vector and aircraft pitch?
2. If that angle is zero degrees, is Pitch the direction your aircraft is moving? (assuming zero crab as well)
Thanks in advance.
2. If that angle is zero degrees, is Pitch the direction your aircraft is moving? (assuming zero crab as well)
Thanks in advance.
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HUD gets its information from the IRS, so it is Earth related, wereas pitch is Air related.
ALPHA:Also α, also angle of attack, the angle between the relative wind and the longitudinal axis of the body, x-z plane, deg.
In other words the flight path vector shows you where you are going
Angle zero, could be in a windshear
HUD gets its information from the IRS, so it is Earth related, wereas pitch is Air related.
ALPHA:Also α, also angle of attack, the angle between the relative wind and the longitudinal axis of the body, x-z plane, deg.
In other words the flight path vector shows you where you are going
Angle zero, could be in a windshear
Last edited by kijangnim; 5th May 2010 at 19:07.
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lol.. how did I know that would be the first response. I thought about that just as I hit the send button.
Let me clarify the Subject.
Heads Up Display Pilots - Question
1. What is the definition of the angle made between the Flight Path Vector and aircraft pitch?
2. If that angle is zero degrees, is Pitch the direction your aircraft is moving? (assuming zero crab as well)
(I know, stupid questions, but I'm clearing up an argument with a stubborn Microsoft wannabe)
edit: thanks for your edit kijangnim. I have another reply awaiting mod review due to links. Hopefully it will be up soon.
Let me clarify the Subject.
Heads Up Display Pilots - Question
1. What is the definition of the angle made between the Flight Path Vector and aircraft pitch?
2. If that angle is zero degrees, is Pitch the direction your aircraft is moving? (assuming zero crab as well)
(I know, stupid questions, but I'm clearing up an argument with a stubborn Microsoft wannabe)
edit: thanks for your edit kijangnim. I have another reply awaiting mod review due to links. Hopefully it will be up soon.
1. On my steed (DHC-8 Q400 with Rockwell Collins HGS 4100) the angle between Aircraft reference and Flight path symbols has no definition or use. As flight path is IRS derived, flight path symbol shows flightpath relative to earth. Vertical angle between ac reference (pitch) and flight path is roughly equal to AoA on aeroplanes with wing incidence angles close to zero and when there are
no significant vertical air currents (updrafts or downdrafts).
2. Yup, you can say so. If flightpath and pitch symbol line-up, aeroplane is flying where the nose is pointing (relative to earth). It's hard to achieve it in normal flight, though. All the aeroplanes I've flown have cruised with some positive pitch.
no significant vertical air currents (updrafts or downdrafts).
2. Yup, you can say so. If flightpath and pitch symbol line-up, aeroplane is flying where the nose is pointing (relative to earth). It's hard to achieve it in normal flight, though. All the aeroplanes I've flown have cruised with some positive pitch.
Gender Faculty Specialist
It's not AoA.
It's the angle between the pitch attitutde of the aircraft and the aircraft vector, it might be close enough but it is NOT AoA.
It's not defined anywhere as far as I can see, Embraer 195.
Angle of attack is defined as the angle between the mean aerodynamic chord of the wing and the freestream airflow. NOT pitch attitude and freestream airflow. For example, you can have an aircraft with zero pitch attitude but still have a positive angle of attack.
It's the angle between the pitch attitutde of the aircraft and the aircraft vector, it might be close enough but it is NOT AoA.
It's not defined anywhere as far as I can see, Embraer 195.
Angle of attack is defined as the angle between the mean aerodynamic chord of the wing and the freestream airflow. NOT pitch attitude and freestream airflow. For example, you can have an aircraft with zero pitch attitude but still have a positive angle of attack.
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I guess since I'm new, my posts are being mod reviewed if I make a post with a link.
I have two posts in queue with links.
The same argument is developing here which developed between a Microsoft wannabe and me. (which is the reason for this thread explained in a post which is still awaiting mod review from yesterday. The microsoft wannabe wasn't convinced with all the sources I provided for him and wanted a thread at pprune,).
I'll try to attach a diagram from Boeing. Hopefully this will clear it up? (and hopefully it doesn't get put into the mod queue).
Since I can't post links yet, just google "Angle Of Attack" + "Flight Path Vector" + "Pitch".. You'll find the same Boeing document in the first or second hit (along with a long list of other sources including a US Patent from 1971), who explain AOA for an aircraft is Aircraft pitch relative to FPV.
Also, if you've never flown a Heads Up Display, or if your aircraft doesn't have one (or an AOA indicator), you may still think AOA is defined only as Wing chord to relative wind. It's not. The aircraft as a whole also has an AOA. It is defined as the difference between Pitch and the Flight Path Vector. The generic definition for AOA as pointed out in the first reply by kijangnim.
I have two posts in queue with links.
The same argument is developing here which developed between a Microsoft wannabe and me. (which is the reason for this thread explained in a post which is still awaiting mod review from yesterday. The microsoft wannabe wasn't convinced with all the sources I provided for him and wanted a thread at pprune,).
I'll try to attach a diagram from Boeing. Hopefully this will clear it up? (and hopefully it doesn't get put into the mod queue).
Since I can't post links yet, just google "Angle Of Attack" + "Flight Path Vector" + "Pitch".. You'll find the same Boeing document in the first or second hit (along with a long list of other sources including a US Patent from 1971), who explain AOA for an aircraft is Aircraft pitch relative to FPV.
Also, if you've never flown a Heads Up Display, or if your aircraft doesn't have one (or an AOA indicator), you may still think AOA is defined only as Wing chord to relative wind. It's not. The aircraft as a whole also has an AOA. It is defined as the difference between Pitch and the Flight Path Vector. The generic definition for AOA as pointed out in the first reply by kijangnim.
ALPHA:Also α, also angle of attack, the angle between the relative wind and the longitudinal axis of the body, x-z plane, deg.
Gender Faculty Specialist
Well if you put it like that then anything has got an angle of attack if it's moving! Which I agree with.
The important angle of attack, and the one that we are referring to when we talk about it, is the angle of attack of the wing. The AoA of the wing is variable along it's span due to wash out.
You first asked what the angle between the flight path vector and the pitch indicator on the HUD was. It is the difference between the aircraft pitch attitude and the aircraft flight path. It is not an angle of attack indicator.
Link
The important angle of attack, and the one that we are referring to when we talk about it, is the angle of attack of the wing. The AoA of the wing is variable along it's span due to wash out.
You first asked what the angle between the flight path vector and the pitch indicator on the HUD was. It is the difference between the aircraft pitch attitude and the aircraft flight path. It is not an angle of attack indicator.
Link
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Angle of Attack on a HUD is the difference between the Flight Path Vector (Indicator) and the waterline marker (aircraft symbol). If the HUD has an Angle Of Attack Indicator as well, it will represent the angle between your FPV and Waterline marker.
Ask anyone who fly's a HUD.
Unfortunately, I don't think I can post links yet, but please google "Angle Of Attack" + "Flight Path Vector" + "Pitch" and post the link of the second hit which is a pdf from Boeing titled "What Is Angle Of Attack".
Here is a quote.Of course we all know the definition of Wing/airfoil AOA. The questions asked above are in reference to the aircraft as a whole.
Scroll down on your aerospaceweb source with the picture of the 747.
Ask anyone who fly's a HUD.
Unfortunately, I don't think I can post links yet, but please google "Angle Of Attack" + "Flight Path Vector" + "Pitch" and post the link of the second hit which is a pdf from Boeing titled "What Is Angle Of Attack".
Here is a quote.
"Most commercial jet airplanes
use the fuselage centerline or
longitudinal axis as the reference
line."
use the fuselage centerline or
longitudinal axis as the reference
line."
Scroll down on your aerospaceweb source with the picture of the 747.
"The following picture illustrates the definitions of angle of attack a, measured with respect to the velocity vector, and pitch angle q, measured with respect to the horizon."
Gender Faculty Specialist
Here's your link
My HUD doesn't have an AoA indicator. We have no reference for AoA and don't need it. If you're in a Typhoon or something similar then you do use it.
Consider this. An airliner flying at 250kts at a constant altitude will have a pitch attitude of, say, 5 degrees. An AoA of, say, 10 degrees.
Now you slow down to 150kts an extend a bit of flap. You maintain your constant altitude. Your pitch attitude can be maintained at 5 degrees because you're extending flap.
Now, what is your AoA? Bearing in mind the lift equation which basically states that if you reduce speed you must increase your angle of attack to maintain your altitude.
Your AoA will be more than the 10 degrees required for 250kts. Say 15 degrees for arguments sake.
But, the indications on the HUD of the aircraft pitch and the flight path vector will be the same.
My HUD doesn't have an AoA indicator. We have no reference for AoA and don't need it. If you're in a Typhoon or something similar then you do use it.
Consider this. An airliner flying at 250kts at a constant altitude will have a pitch attitude of, say, 5 degrees. An AoA of, say, 10 degrees.
Now you slow down to 150kts an extend a bit of flap. You maintain your constant altitude. Your pitch attitude can be maintained at 5 degrees because you're extending flap.
Now, what is your AoA? Bearing in mind the lift equation which basically states that if you reduce speed you must increase your angle of attack to maintain your altitude.
Your AoA will be more than the 10 degrees required for 250kts. Say 15 degrees for arguments sake.
But, the indications on the HUD of the aircraft pitch and the flight path vector will be the same.
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Thanks for posting the link Chesty.
AOA of the aircraft is the same as it was before you extended the flaps because your resultant velocity vector/flight path vector hasn't changed nor has your pitch. AOA of your wing may have changed along the area of the wing where the flaps are extended.
(I say may have as flaps are also used to increase surface area/aspect ratio of the wing, thereby creating more lift without having to increase wing root AOA. Fowler flap/slats are a good example)
Lets get back to basics of the original post Chesty.
AOA for an aircraft is defined as the angle between it's Pitch and it's flight path vector.
Do you disagree with the above definition or do you think no such definition exists or is "stupid"?
AOA of the aircraft is the same as it was before you extended the flaps because your resultant velocity vector/flight path vector hasn't changed nor has your pitch. AOA of your wing may have changed along the area of the wing where the flaps are extended.
(I say may have as flaps are also used to increase surface area/aspect ratio of the wing, thereby creating more lift without having to increase wing root AOA. Fowler flap/slats are a good example)
Lets get back to basics of the original post Chesty.
AOA for an aircraft is defined as the angle between it's Pitch and it's flight path vector.
Do you disagree with the above definition or do you think no such definition exists or is "stupid"?
Gender Faculty Specialist
I don't entirely disagree.
I understand what your definition is saying however, the most important angle we talk about is the angle of attack of the wing. That's the one that'll kill you and that's the one that we need to stay flying.
We need to change the angle of attack of the wing to maintain or change the amount of lift that we require. The AoA of the aircraft is only relevant because it's attached to the wing and changing one will change the other. Untill you involve the slats and flaps.
You could probably design an aircraft which would fly around with an aircraft AoA of 90 degrees whilst the wing AoA remained within the safe and usable limits that it is intended to. I grant you it would look rather odd though!
I understand what your definition is saying however, the most important angle we talk about is the angle of attack of the wing. That's the one that'll kill you and that's the one that we need to stay flying.
We need to change the angle of attack of the wing to maintain or change the amount of lift that we require. The AoA of the aircraft is only relevant because it's attached to the wing and changing one will change the other. Untill you involve the slats and flaps.
You could probably design an aircraft which would fly around with an aircraft AoA of 90 degrees whilst the wing AoA remained within the safe and usable limits that it is intended to. I grant you it would look rather odd though!
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Yes, I agree with what you're saying.
Critical Angle of Attack is associated with the wing. You will have no argument from me.
But keep in mind, the Critical Angle of Attack can be referenced to the wing or the fuse centerline. It doesn't really matter as long as your stick shaker/stall warning... (whatever), starts to tell you, "Hey moron, stop pitching up and add some power!"
Most commercial aircraft use the fuse centerline as the reference for AOA, As noted in the Boeing pdf. Due to exactly what you stated, wing washout.
But just so long as we agree that aircraft AOA is defined as the angle made between Pitch and the FPV, we're all happy (except for the Microsoft idiot I been arguing with... I know, I shouldn't even waste my time.. don't ask).
Reverse what you just said, and you have a Helicopter or Osprey..
And I agree, they do look rather odd. A million parts all flying in formation? No thanks!
(just kidding helo drivers)
:-)
(by the way, how many posts do you need to start posting links?)
Thanks again for your help in posting the links Chesty.
Critical Angle of Attack is associated with the wing. You will have no argument from me.
But keep in mind, the Critical Angle of Attack can be referenced to the wing or the fuse centerline. It doesn't really matter as long as your stick shaker/stall warning... (whatever), starts to tell you, "Hey moron, stop pitching up and add some power!"
Most commercial aircraft use the fuse centerline as the reference for AOA, As noted in the Boeing pdf. Due to exactly what you stated, wing washout.
But just so long as we agree that aircraft AOA is defined as the angle made between Pitch and the FPV, we're all happy (except for the Microsoft idiot I been arguing with... I know, I shouldn't even waste my time.. don't ask).
You could probably design an aircraft which would fly around with an aircraft AoA of 90 degrees whilst the wing AoA remained within the safe and usable limits that it is intended to. I grant you it would look rather odd though!
And I agree, they do look rather odd. A million parts all flying in formation? No thanks!
(just kidding helo drivers)
:-)
(by the way, how many posts do you need to start posting links?)
Thanks again for your help in posting the links Chesty.
Gender Faculty Specialist
Reverse what you just said
One question.
How can you reference critical angle of attack to the aircraft AoA if you are changing the wing AoA with flaps and slats?
The wing angle of attack has already been increased by flaps whilst you can maintain the same pitch (your aircraft AoA). The stalling angle of attack of the wing is actually slightly less with flaps extended. And you will, therefore, stall the wing at a lower aircraft AoA/pitch than you would in a clean configuration.
So, whilst I understand the definition that you're using, to me that would appear to by less than clever.
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How can you reference critical angle of attack to the aircraft AoA if you are changing the wing AoA with flaps and slats?
"It's all electrons these day my friend." - I forget who said it.
The onboard computers, depending on your aircraft, calculate Critical Angle Of Attack referenced to the fuse centerline, which is referenced to your aircraft configuration.
By the way, you said you fly a HUD without an AOA indicator. Not sure how long you been flying it, but look in the manual, you'll find the AOA of your aircraft is the angle between your Pitch and FPV. If it's not in the manual, ask the CP, when he is wrong, ask an Instructor at your company (preferably, prior military). Then go back to the CP and rub it in his face. :-)
